In recent years, there has been an extensive investigation on NO as a biomarker. One such use of the biomarker is in the detection of respiratory inflammation such as asthma. The concentration of nitric oxide (NO) in exhaled breath serves as a marker of the inflammation in the airways of asthma patients. Thus the use of exhaled NO (eNO) is considered as a promising tool in diagnosing asthma. However, the concentration of eNO in the breath is very low. In a healthy adult the concentration is about 10-35 ppb (parts per billion) of NO whereas in children the concentration is about 5-25 ppb. An individual with considerable amount of inflammation has above 70-100 ppb.
Sensors using electrochemical methods to detect NO have previously been shown. However for measurements of exhaled NO, they lack the combination of fast response, small size and high sensitivity. Conventional electrochemical sensors can detect gas concentration down to some parts per billion but they suffer from long response times, typically in the order of 60-100 s. Consequently they require complicated flow handling and buffering of the exhaled breath sample.